EP0103172B1 - Device for determining the viscosity of liquids, especially of blood plasma - Google Patents

Abstract

An apparatus for determining the viscosity of fluids, particularly blood plasma, includes an outer housing including a front surface having a groove therein; a disposable capillary tube removably mounted in the groove and including at least one loop, each of the loops having two substantially horizontal branches including an upper branch and a lower branch for flowing the fluid under the influence of gravity through a predetermined path, and a device for measuring the rate of flow of the fluid along the path in one of the horizontal branches. Also disclosed is a flexible disposable capillary tube for the fluid viscosity measuring apparatus.

Description

The invention relates to a device for determining the viscosity of liquids, in particular blood plasma, according to the preamble of claim 1.

From FR-A 775 672 a device of the type mentioned at the outset is known with which the viscosities of liquids can be determined.

Blood can be regarded as an independent, moving organ, which is a suspension of various cells in the plasma as a continuous phase. It is said to essentially carry the blood cells and the plasma through all parts of the vessel bed. Fats, electrolytes and especially proteins are found in this plasma. The blood is used by mass and heat transport to maintain a so-called. Flow equilibrium, which is adapted to the respective organs or their cells. For example, the increased need for energy is met by increasing blood flow and thus increasing the supply of oxygen, glucose or fatty acids, while at the same time taking care of the removal of metabolic intermediates and end products. If for some reason such a steady state cannot be maintained over a long period of time, the organism is not viable.

To maintain this vital flow equilibrium, a volume flow must be adapted to the respective requirements

For this purpose, the driving pressure Ap is ultimately determined by the pumping power of the heart, while the whole _blood viscosity η _blood and the vessel geometry (I = length, r = vessel radius) determine the hydrodynamic resistance of the flow channel.

An intensive investigation of the influence of whole blood viscosity on the flow behavior of blood in recent years has clearly shown that under pathological conditions this size can be the limiting factor for perfusion.

The apparent viscosity of the blood, which is a non-Newtonian fluid, is essentially determined by the following factors, namely the plasma viscosity, the hematocrit value (volume fraction of the blood cells in the whole blood), the aggregation of the erythrocytes and the deformability of the erythrocytes. Each of these factors, including the plasma viscosity, plays an important role in the detection of diseases in the blood and should therefore be determined as simply and precisely as possible in routine medical operation.

The following types of viscometers are essentially known for quantifying the plasma viscosity, namely the falling ball, the rotating and the capillary viscometer, the measuring devices currently used being only poorly suited for routine medical operation for the reasons explained below.

The design of the falling ball viscometer is based on Stokes' theoretical approach, according to which the following applies to the resistance of a flow around a ball:

und der Zeit t, die die Kugel benötigt, um eine definierte Strecke I zurückzulegen, wobei die mittlere Geschwindigkeit _VK = I/t ist, ergibt sich die Viskosität:

üblicherweise wird der Ausdruck 2/9 r_K ²/₁ g in die experimentell bestimmte Gerätekonstante K einbezogen, so dass sich empirisch die Viskosität bestimmen lässt.After a short start-up distance, the ball sinks at a constant speed in the fluid. The gravity of the ball with the density _{9K is kept} in balance by the buoyancy force and the friction force F _w . From the equation

and the time t that the ball needs to travel a defined distance I, where the average speed _VK = I / t, the viscosity results:

usually, the term 2/9 r _{K ^2/1} g included in the experimentally determined device constant K, so that the empirical viscosity can be determined.

However, the measurement inaccuracies in this method are relatively large due to the visual timing and can be avoided by opto-electronic measures.

It must also be taken into account that the theory on which this method is based requires that the creeping flow be maintained and therefore requires the use of relatively large balls. Associated with this is a filling volume of at least 50 ml of plasma, which corresponds to a required blood volume of approximately 100 ml. Such a blood sample usually represents an unreasonable burden for the patient, especially if the frequently necessary performance of several measurements (measurement of further parameters; therapy monitoring) should be necessary.

wobei

The second method to determine plasma viscosity is rotary viscometry. The plasma viscosity results from the following formula

in which

The device constant, which depends on the type of measuring chamber used, represents a multitude of sources of error that can be traced back to the type and processing of the measuring chamber.

The first group of such viscometers consists of an arrangement of coaxial cylinders , for example the GDM viscometer (Gilinson-Dauwalter-Merrill), while the second group has a plate-cone arrangement, for example the Wells-Brookfield viscometer.

A frequently used rotary viscometer uses both of the chamber arrangements mentioned, namely the so-called. Mooney configuration. These are coaxial cylinders that are designed as a plate and cone system on the top and bottom. Other designs of the chamber geometry are, for example, the Rhombo-Spheroid Viscometer from Dintenfass or the Rheogoniometer from Weissenberg.

For most rotary viscometers, the speed is specified via a manual transmission and the torque that is removed, which is set as a function of the plasma viscosity, is measured. In contrast, the Deer rotational rheometer (Mooney configuration) works with a specified torque, whereby the speed output is measured.

Since the theory of the rotary viscometer presupposes a stationary shear flow in the annular gap, the inner and outer cylinders have to be manufactured very precisely in order to ensure good reproducibility of the measurements. In addition, the chamber must be cleaned carefully after each measurement without leaving any residues of the cleaning agent in the chamber. Because such residues of the measuring solution and the cleaning agent change the wettability of the surfaces of the measuring chamber, which is directly involved in the measurement. In addition, about 15 ml of plasma are required per measurement, which corresponds to about 30 ml of whole blood. Since several measurements are usually carried out to determine the mean, this means that larger amounts of blood have to be taken from the patient, which is an increased burden for him and is therefore undesirable.

wobei

The best-known method for measuring the viscosity of plasmas consists in determining the outflow time or the volume flow V, which is measured in a capillary viscometer. According to Hagen-Poiseuille, the following applies to the average speed in a capillary:

in which

According to this law, all types of capillary viscometers determine the plasma viscosity. The average speed v = I / t is determined by measuring the time it takes for the plasma to travel a defined distance I. Since the geometry of the capillary _(r;, I) is fixed, at a known Ap, the viscosity can be calculated.

The Harkness capillary viscometer, for example, specifies a constant differential pressure Ap via a vacuum pump in a horizontally arranged capillary.

The Ubbelohde viscometer is also known, in which the weight of the plasma column is used as the driving pressure.

Another viscometer with continuously variable pressure was developed by Martin et al. developed.

The Ostwald capillary viscometer, which is often used in technology, consists of a U-tube capillary with vertically arranged legs and is characterized by a precisely reproducible measurement volume with pressures that can also be precisely adjusted.

All these capillary viscometers have in common that they require a complex apparatus structure, which is due to the often only very short measuring time and thus an extensive detector device. In addition, the capillaries used are difficult to manufacture, so that measurement errors arise as a result of the manufacturing tolerances, and since they consist regularly of glass, they have to be thermostatted over a longer period of time, so that they are only available to a limited extent. In addition, the cleaning of such a measuring capillary, as already explained above, represents a further disadvantage since it has to be carried out very precisely and only completely residue-free capillaries can be used. Furthermore, with vertically arranged capillaries there is the disadvantage that drop formation can occur at the outlet end, which falsifies the measuring time of the liquid column passing through the capillary due to the counteracting surface tension of the drop, so that such a capillary must have special, difficult-to-manufacture connecting pieces.

From the already mentioned FR-A 775 672 a device for determining the viscosity is known, which has a vertical capillary tube, to which a liquid reservoir designed as a horizontal tube piece is connected at the top and a measuring chamber at the bottom. As a result of the vertical arrangement of the capillary, it must be made very narrow in order to prevent the liquid in the capillary from flowing too quickly. This inevitably leads to special flow conditions in the capillary, since the flow speed is essentially determined by the capillary and adhesive forces in the capillary.

Furthermore, the driving pressure does not remain the same in this vertical arrangement, since the content of the liquid reservoir and, moreover, the liquid column present in the capillary constantly change.

Finally, a solid material, ie usually glass, is used as the measuring capillary, which, on the one hand, is difficult to manufacture with the necessary precision and, on the other hand, cannot be produced once due to the high manufacturing costs can be thrown away after use. In this respect, such a capillary must be cleaned after each measurement. The residues that inevitably occur in this case often lead to a falsification of the subsequent measurement results, so that such a capillary is then not suitable for determining precise viscosity values.

From US-A 4083 363 it is known to use an elastic capillary tube designed as a disposable article as a suction tube in a device for determining the viscosity of blood.

The invention is based on the object of developing the device of the type mentioned at the outset such that even fast-flowing liquids in relatively wide capillaries can be determined precisely and reproducibly in their viscosity in relatively short time intervals, cleaning work being dispensed with.

This object is achieved by the characterizing features of claim 1.

The device according to the invention also allows the viscosity of fast-flowing liquids, such as blood plasma, to be measured, since on the one hand the driving height is relatively low and on the other hand the length of the horizontal capillary tube portions, which slows down the flow velocity, is relatively large. The measuring arrangement according to the invention is designed in such a way that the driving height remains constant during the measuring process, which leads to a constant flow speed within the measuring capillaries and to constant measured values.

According to the so-called. Disposable capillaries are used, i.e. the capillary is manufactured as a cheap item and is thrown away after use. A flexible plastic hose that can be manufactured with the required tolerances is suitable for these purposes. Such plastic materials advantageously do not interact with the liquids to be examined in the measurement time, that is to say they do not give any plasticizers or the like. to the liquid.

Such a capillary tube is inserted into a groove of a plate which is shaped in accordance with the desired capillary guide and holds the capillary tube securely. The preferred capillary guide is that the capillary tube is placed in at least two capillary tube parts, the respective capillary tube parts being arranged essentially parallel and horizontally. The radius between the capillary tube parts is dimensioned in such a way that pinching or kinking of the capillary tube is reliably prevented.

The diameter of the capillary is selected so that the column of the liquid to be examined neither tears off when it flows through the capillary, nor closes the capillary due to the surface tension and does not flow through it. For the latter purpose, the inlet end of the capillary is advantageously designed as a so-called acceleration section and designed in such a way that a substantially vertical branch is guided from the upper horizontal branch to the inlet opening. After passing through this acceleration section, in which the static friction of the fluid in the tube is surely overcome at the start of the measurement, the liquid enters the horizontally arranged capillary tube part, the first part of which is advantageously designed as a flow or calming section. After passing through the calming section, it is ensured that there is a steady flow in the tube capillary, which can be subjected to the actual measurement.

As a result of the measuring section arranged in loops, which is arranged essentially in a horizontal plane, there is a constant driving pressure difference Ap during the measurement, which is due to the height difference between the individual horizontally arranged branches. While in the prior art an essentially vertical capillary is used, which is flowed through in the shortest possible time, in contrast, according to the invention, there is a capillary arrangement which consists of both a vertically arranged and a horizontally arranged part, both parts being accommodated in the smallest area. This is achieved in that the tube capillary is arranged in a meandering shape or in loops arranged in opposite directions. Thus, the flow of a liquid in a substantially horizontal tube and the flow of a liquid in a substantially vertical tube overlap. The consequence of this is that the measuring times in such an arrangement are considerably longer than the measuring times in an exclusively vertically arranged measuring section. This significantly reduces the measurement errors and the measurement times can be measured much better and more precisely than with a vertical arrangement.

In a further advantageous embodiment, the tube capillary has an ascending section at its end, which prevents the liquid to be examined from flowing out and / or that outflowing liquid forms drops which falsify the measuring times, as explained above.

After the measurement, the tube is removed from the groove of the plate and either kept for further determinations of the liquid or thrown away. There are therefore no leakage effects. Furthermore, no cleaning of the tube capillary is necessary, so that the negative effects mentioned at the outset can be completely avoided.

• Fig. 1 eine schematische Vorderansicht einer ersten Ausführungsform der erfindungsgemässen Vorrichtung,
• Fig. 2 eine schematische Vorderansicht einer zweiten Ausführungsform der erfindungsgemässen Vorrichtung und
• Fig. 3 eine schematische Vorderansicht einer weiteren Ausführungsform, die im wesentlichen der in Fig. 1 gezeigten Vorrichtung ähnelt.

A further explanation of the invention is given by the following description of three exemplary embodiments with reference to the drawing. Show it:

• 1 is a schematic front view of a first embodiment of the device according to the invention,
• Fig. 2 is a schematic front view of a second embodiment of the device according to the invention and
• Fig. 3 is a schematic front view of another embodiment which is substantially similar to the device shown in Fig. 1.

The first embodiment shown in FIG. 1 essentially consists of a housing 10 which has an inclined or preferably vertically arranged front plate 12. The electronic control device and the like are in the housing 10. arranged.

The front side 14 of the front plate has a groove 16 machined therein, which extends from an inlet end 18 to an outlet end 20.

In the embodiment shown in FIG. 1, the groove extends from the inlet end 18 into a substantially vertically arranged capillary tube part 22, which serves as an acceleration area.

This capillary tube part 22 is adjoined by a first horizontal capillary tube part 24, which is divided into a calming section labeled A and a measuring section labeled B.

This capillary tube part 24 merges into a curved capillary tube part 26, which is continued in a second capillary tube part 28, which in turn is advantageously arranged horizontally.

In the particularly preferred embodiment shown in FIG. 1, the capillary tube part 28 is followed by a second curved capillary tube part 30, which in turn is continued in a substantially horizontally arranged third capillary tube part 32. This capillary tube part 32 is considerably longer than the capillary tube parts 24 and 28 and advantageously dimensioned such that its length corresponds approximately to the length of the capillary tube parts 22, 24 and 28 and of the curved capillary tube part 26.

According to a preferred embodiment, the capillary tube part 32 is followed by a capillary tube part 34 which is essentially designed as a rising path and which is returned to the outlet end 20.

It should be added that the capillary tube parts 22 and 34 are only present in a preferred embodiment, i.e. that the capillary tube parts 24 and 32 can also run out substantially horizontally to the inlet and outlet ends.

Furthermore, the embodiment shown in FIG. 1 is not limited to an arrangement of two curved capillary tube parts 26 and 30. Rather, it can also have only one curved capillary tube part 26, so that the capillary tube part 28 already represents the outlet branch. However, this embodiment is less preferred, since the length of the groove is only sufficient to effectively measure the viscosity due to the miniaturization of the device.

The groove 16 is worked in such a way that a hose 36 can be inserted with a precise fit, as can be seen from the enlarged perspective sectional view shown in FIG. 1.

The hose 36 runs from the inlet end 18 to the outlet end 20 in the groove 16 in such a precise manner that there are no kinks or constrictions in it, that is to say the cross section of the hose remains essentially unchanged over its entire length.

Thus, the depth and the width of the groove 36 essentially correspond to the hose diameter. It has proven to be advantageous that the tube has an essentially circular cross section, the inner diameter being approximately 0.5-2 mm, preferably approximately 0.7-1.0 mm.

In order to obtain the best possible temperature compensation between the advantageously thermostatted front plate 12, which is explained below, the wall thickness of the hose is approximately 0.2-0.5 mm, preferably 0.3-0.4 mm.

A transparent plastic material which is translucent is advantageously used as the hose material, so that the liquid fronts occurring in the hose can be detected with the aid of optical sensors. Polyurethane and polyethylene, which are essentially free of plasticizers, are used as preferred plastic materials. Particularly preferred is polyurethane, which can be delivered in the desired tolerances and which provides reproducible measurement results to a high degree.

For the exact insertion of the hose into the groove 16, a bead can be provided at its beginning, which can be inserted into a recess 38 in the front plate 12, which is arranged in the region of the inlet end 18. This enables exact insertion of the hose as well as facilitating the filling of the measuring liquid into the hose.

Two detectors 40 and 42 are provided in the front plate 12 in the area of the capillary tube part 24 of the groove 16, which detectors are preferably designed as light sensors. Advantageously, these light sensors are each inserted into an opening provided in the capillary tube part 24 and do not hinder the insertion of the tube 36 into this capillary tube part 24. These sensors 40 and 42 are so sensitive that they respond to the occurrence of a fluid meniscus and the resulting change in light.

A fill mark 44 is provided in the capillary tube part 28 downstream of the sensor 42, in the immediate vicinity of which a further sensor 46 is provided. This sensor 46 corresponds in type and structure and arrangement to sensors 40 and 42. This sensor 46 controls a locking magnet 48, which is arranged in the vicinity of the outlet end 20, via a line (not shown).

When a signal occurs at the sensor 46, the closure magnet 48 is activated and closes the tube 36 inserted into the groove 16 for a certain time, preferably approximately 0.5-4 min., In particular 1-2 min. This time serves to bring the liquid in the hose 36 to the temperature in the front plate 12 and accordingly in the hose 36, which corresponds to a dry thermostat.

The front plate 12 is equipped with two connections 50 and 52 for thermostatting, which are designed as electrical connections or as pipe connections for the supply of a correspondingly heated liquid originating from a reservoir (not shown). Electrical heating by means of a heating spiral (not shown) provided in the front plate 12, which is connected to the connections 50 and 52, is preferred. These connections 50 and 52 can of course also be accommodated within the housing 10. If blood plasma is to be measured in its viscosity, the front plate 12 and thus the tube 36 are adjusted to the body temperature, i.e. tempered to approx. 37 ° C. When using other liquids, of course, any temperatures can be presented in the front panel, which is preferably made of aluminum.

Furthermore, the front plate 12 has at its lower end a preferably foldable cover 54, which is advantageously made of a transparent plastic material. When the lid is closed, the display 58 can be deleted so that a new value can be measured.

The viscosity measurement is carried out with the device according to the invention according to the following rules and in the following way:

The time t that the liquid, in particular the blood plasma, takes to cover the defined measuring distance B in the tube 36 is measured.

wobei V_pi, = Plasmavolumenstrom, r_s = Radius des Kapillarschlauches, I = Länge der Plasmasäule und η_PI = dynamische Viskosität des Plasmas bedeuten. Mit V_P, = V/t und V = πr_s2 Im ergibt sich die dynamische Viskosität nach Gleichung:

wobei IM = Länge der Messstrecke (B) und t = gemessene Durchflusszeit bedeuten.Assuming a Hagen-Poiseuille flow in the capillary, the volume flow results from the following equation

where V _pi , = plasma volume flow, r _s = radius of the capillary tube, I = length of the plasma column and η _PI = dynamic viscosity of the plasma. With V _P , = V / t and V = πr _s 2 Im, the dynamic viscosity results from the equation:

where IM = length of the measuring section (B) and t = measured flow time.

wobei g = Erdbeschleunigung, Ah = konstruktiv gegebene treibende Höhendifferenz und ζ_PI = Dichte des Plasmas bedeuten.The driving pressure Ap is the hydrostatic pressure of the plasma column, which is given purely geometrically by the elevation of the measuring section compared to the capillary tube part 32. From this follows as the equation for determining the dynamic viscosity η _PI :

where g = acceleration due to gravity, Ah = constructive driving height difference and ζ _PI = density of the plasma.

All constants are combined into one device constant K. This results in:

auch die dynamische Viskosität nach folgender Formel (11) berechnet und als Wert ausgegeben werden:

It can be seen from this formula that the kinematic viscosity _V p _l = η _PI / ζ _PI can be determined and displayed directly by measuring the outflow time. Since the density of the plasma fluctuates only within narrow limits (max. ± 3%), in a simple embodiment - assuming an average plasma density

The dynamic viscosity is also calculated according to the following formula (11) and output as a value:

The measurement error possible due to this simplifying assumption is certainly less than ± 3%.

The measurement is carried out in such a way that the hose 36 is first inserted into the groove 16 in the front plate 12. The liquid to be examined, in particular plasma, which was obtained from the anticoagulated blood taken from the patient, is then in an amount of about 200-400, max. 500 µl introduced into the tube. A 2 ml syringe is preferably used for this purpose, the cannula of which is inserted into the capillary of the tube 36. This cannula closes the capillary tightly so that the liquid only moves forward in the capillary due to the pressure on the plunger of the syringe. The filling of the capillary is completed when the liquid front reaches the filling mark 44.

Subsequently, either the cannula of the syringe remains in the capillary until the filled liquid has warmed to the temperature of the front plate 12, or the cannula is preferably pulled out after filling, so that the liquid front moves up to the sensor 46. As a result, the sensor 46 is actuated, which in turn triggers the closure magnet 48, which squeezes the hose 36, so that the liquid column in the hose 36 can no longer move.

The temperature is controlled for a certain time of about 0.4-4 minutes, in particular 1-2 minutes, and the result is a dry thermostatting of the plasma used to about 37 ° C. After this time, the locking magnet 48 opens automatically and the actual measuring process begins.

The capillary tube part 22 initially serves as an acceleration path in which the static friction of the fluid in the tube 36 is overcome. The liquid then enters the settling section A of the capillary tube part 40, in which an essentially stationary flow is achieved. When passing the first sensor 40, that is, when entering the measuring section B, the measuring process is started, which is then ended, when the liquid front has reached the second sensor 42. The measured time is then output on the display 58 and corresponds to a viscosity value which can be read off on a calibration curve.

After passing through the measuring section B, the flow of the liquid in the lower capillary tube part 32 continues until it is braked by the rise in the capillary tube part 34 and comes to a standstill.

The cover 54, which had closed the front plate 12 during the measurement, is then opened and the tube 36 is removed from the groove 16. The plasma contained in the tube can either be reused or thrown away together with the tube 36. It has proven to be particularly advantageous for the measurement of blood plasma that the measurement section B is approximately 30-200 mm, in particular approximately 80-120 mm long and the geometrically predetermined driving height, that is the vertical distance between the capillary tube part 24 and the capillary tube part 32 , about 40-160, in particular 90-120 mm.

The device can of course also have a programmed calibration curve, so that the display 58 shows the automatically calculated viscosity value. This display advantageously remains until the next measurement.

A new capillary tube is used for each further measurement. This saves all the cleaning processes that are otherwise required and, because of the same wettability in every case, ensures reproducible measurements in an error range of max. ± 2%.

Since the device is very handy, it takes a long time to load, insert and fill the hose, max. about 1 min. Advantageously, all subsequent measurement processes, including the preheating of the plasma, take place automatically and do not require any special operation or presence. This means that the device can be used again for a measurement every 2-3 minutes; Due to its small dimensions, its dry thermostatting and its simple and time-saving handling, it is portable and can therefore be used directly for bedside diagnostics. After a short introduction, it can be operated correctly by any assistant and does not require any cleaning work, so that any number of measurements can be carried out in a short time. Since only an extremely small measuring volume (max. 200 j.tl) is required, the device can be used for daily therapy control without a large patient load.

Another embodiment is shown in Fig. 2, in which like reference numerals represent like parts. The device shown in FIG. 2 allows the determination of the dynamic and kinematic viscosity, since this device is additionally equipped with a density measuring device.

As can be seen from FIG. 2, this device has in its right area the device for determining the viscosity explained above, so that it is no longer explained in detail. Compared to the embodiment described in FIG. 1, the capillary tube part 34 merges again at 60 into a lower, essentially horizontal capillary tube portion 62, which in turn merges into a curved capillary tube part 64, to which a vertical capillary tube part 66 adjoins. Via a curved capillary tube part 68, this capillary tube part is connected to a further, essentially horizontal capillary tube section 70 containing a three-way shut-off element 72. This three-way shut-off device 72 arranged laterally on the front plate 12 can, however, also be accommodated in the housing 10, the hose 36 being connected accordingly.

Thus, according to this second embodiment, the groove 16 and the hose 36 extend to the three-way shut-off device 72, which either releases the hose 36 for ventilation or else establishes a fluid connection with a suction pump 76 via a line 74. This three-way shut-off device 72 is set to “venting” during the viscosity measurement described above.

However, if the density of the liquid is to be measured, after the viscosity value has been determined, the three-way shut-off device 72 is automatically switched over, the connection to the suction pump 76 being established.

The density measurement is carried out as follows: A negative pressure is applied to the plasma column in the tube 36, which pulls it up into the left part of the measuring arrangement, ie into the capillary tube parts 34, 62, 66 and the like. 70. For this purpose, an increasing vacuum is required with increasing height, which is supplied by the suction pump 76. In order to ensure a reliable measurement, the driving height, which is determined by the vertical distance between the capillary tube sections 62 u. 70 is determined, chosen to be significantly larger than the driving height used for viscosity measurement. It is, for example, about 60-120, in particular 80-100 mm.

First, the liquid column located in the capillary tube part 34 is sucked into the capillary tube portion 62 by means of negative pressure, in which a sensor 78 is arranged, which is preferably designed as an optoelectronic sensor. This sensor 78 is used to determine a first pressure value _{P1 '} which is either output on the display 58 or is stored in a corresponding electronic holding circuit. The liquid is then sucked into the upper capillary tube section 70 with an increased suction pressure, in which a sensor 82 is in turn arranged, which has the same configuration as the sensor 78 mentioned above. These sensors 78 and 82 advantageously correspond to sensors 40, 42 and 46.

zu der gewünschten Dichte ζ führt.The second measured value _P2 measured at the sensor 82 is also determined, the difference between these measured values according to the following equation (12)

leads to the desired density ζ.

The advantage of the greater driving height is the significantly lower influence of the wettability of the hose 36, which is otherwise eliminated in the above difference formation. The height h _j -h ₂ represents the distance of the capillary tube section 62 or 70 from the meniscus of the liquid, which is located in the capillary tube 34. This meniscus height is determined by the entire arrangement of the hose and the feeding of the liquid up to the filling mark.

In a further embodiment, which is essentially based on that of FIG. 1, the outlet end 20 is connected to the three-way shut-off device 72, which is connected to a pressure pump, not shown. In this density measurement, the liquid column in the capillary tube part 28 u. 24 driven back by excess pressure, the sensors 46 or 42 and 40 being used to determine the pressure values _P1 or _P2 . However, this embodiment is not preferred over the embodiment described above.

bestimmt werden, so dass hierdurch die wichtigsten rheologischen Parameter einer Flüssigkeit in einer einfachen und unkompliziert zu handhabenden Vorrichtung bestimmt werden können.By determining the density ζ _p1 and the dynamic viscosity mentioned above, it is possible to use the equation

be determined so that the most important rheological parameters of a liquid can be determined in a simple and uncomplicated device.

In addition to determining the viscosity, it is possible to make a direct statement about the total protein content in the plasma with just one measurement of the plasma density.

A comparison of the plasma viscosities determined with the calibration curve shows that the values determined in this way correspond very well with the values recorded with a Coulter-Harkness viscometer. The deviations of the measured values are approximately ± 0.5%.

FIG. 3 shows another particularly preferred embodiment of a viscometer according to the invention at 80, this embodiment being essentially similar to the embodiment shown in FIG. 1. In this respect, reference is made to the above statements relating to FIG. 1.

The viscometer 80 according to FIG. 3 essentially consists of a housing 82 which has an advantageously inclined front plate 84.

This front plate 84 corresponds essentially to the front plate 12 of FIG. 1. Accordingly, a groove 86 is again provided in this front plate 84, which extends from the inlet end 88 to the outlet end 90. This groove 86 includes a first horizontal capillary tube part 92, a capillary tube part 94 adjoining it, bent by a substantially right angle, a capillary tube part 96 adjoining the capillary tube part 94, again bent by a substantially right angle, a capillary tube part 96 96 subsequent capillary tube part 98 bent at a right angle, a capillary tube part 100 adjoining the capillary tube part 98, essentially bent at a right angle, and a capillary tube part 102 adjoining the capillary tube part 100, essentially bent at a right angle Capillary tube parts 92 to 100 have an S-shape, while the capillary tube part 102 rises at least up to the height of the capillary tube part 92.

The capillary tube parts 92, 96 and 100 and the capillary tube parts 94, 98 and 102 are arranged essentially parallel to one another. However, the capillary tube parts 94 and 98 can also assume an essentially semicircular shape, that is to say a loop shape. It is only important here that the essentially rectangular transitions of the groove 86 do not kink the capillary tube 104 to be inserted into this groove, which corresponds to the capillary tube 36.

A slightly enlarged groove 106 is arranged upstream of this groove 86, into which a syringe 108 can be inserted.

This syringe 108 is advantageously connected to the capillary tube 104 and, filled with the plasma, is inserted into these grooves 86 and 106.

This embodiment, too, in turn has a calming section denoted by A, which essentially extends in the capillary tube parts 94 and 96.

The measuring section B, which corresponds in length to the capillary tube part 32 according to FIG. 1, is located in the l (apillary tube part 100).

With regard to the arrangement of the capillary tube parts 92 to 102, reference is made to the description of FIG. 1. The capillary tube part 102 in turn represents an ascending section and thus corresponds to the capillary tube part 34 according to FIG. 1.

When comparing the two embodiments according to FIGS. 1 and 3, it can be seen that the capillary tube part 22 is omitted in FIG. 3 and that the measuring section has been moved from the capillary tube part 24 into the lower capillary tube part 100. This relocation is due to the arrangement of the syringe 106, which according to a preferred embodiment can be emptied accordingly with a syringe drive 110. This syringe drive 110 is arranged in the front plate 94 and is located in the longitudinal axis of the capillary tube part 92.

With regard to the shape and shape of the groove 86 and the dimension and material of the hose, reference is made to the description of FIG. 1.

3 detectors 112, 114 and 116 are again provided in the front plate 84, the de tector 112 in the capillary tube part 98, advantageously at its lower end, provided and the detectors 114 u. 116 are provided in the capillary tube part 100. These detectors 114, 116 are preferably again designed as light sensors and are correspondingly located in the capillary tube parts 98 u. 100 inserted into the provided openings and thus do not hinder the insertion of the tubular capillary tube 104. Otherwise, these detectors correspond in design and arrangement to detectors 40, 42 and 46, so that reference is again made to the description of FIG. 1.

Detector 112 is preferably electronically coupled to the syringe drive and stops this syringe drive as soon as the plasma pumped into capillary tube 104 has reached detector 112. Accordingly, the filling process started when the cover 54 is closed according to FIG. 1 is interrupted for a certain time during which the plasma is in the capillary tube parts 94, 96 and. 98 located. With regard to the interruption times, reference is made to the description of FIG. 1.

If the plasma contained in the calming section A has been tempered to the desired temperature after this time, a tube cutting tool 118 is actuated, which is arranged on the capillary tube 92 and cuts through the capillary tube 104 contained in the groove 86. As a result of the separation from the closed syringe 108, the plasma contained in the calming section A can continue to flow due to gravity and thus reaches the measuring section B.

As explained above, this measuring path B is formed between the detectors 114 and 116 and thus corresponds to the measuring path B of FIG. 1, which is formed between the detectors 40 and 42. Otherwise, the thermostatting and the measurement of the viscosity also correspond to the embodiment according to FIG. 1, so that reference is made to this.

Claims (16)

1. Apparatus for measuring the viscosity of fluids, in particular of blood plasma, comprising a capillary tube for passing said fluid under the influence of gravity, whereby said capillary tube comprises vertical and horizontal capillary tube branches (22, 24, 26, 28, 30, 32, 34; 60, 62, 64, 66, 68, 70; 90, 92, 94, 96, 98, 100, 102), and with a means for measuring the rate of flow, characterized in that said capillary tube comprises at least two horizontally arranged straight capillary tube branches (24,28; 96, 100) in form of at least a first and at least a second capillary tube branch, one of which comprising the measuring path (B), and which are connected via a vertically arranged capillary tube branch (26; 98), and that it is embodied as flexible plastic hose being exchangeably arranged within a respectively shaped groove (16; 86) of a front plate (12; 84).

2. Apparatus according to claim 1, characterized in that the second capillary tube branch (28) is connected with a third horizontally arranged capillary tube branch (32) via a lower curved capillary tube branch (30).

3. Apparatus according to claim 1 or 2, characterized in that at the first capillary tube branch (24) two detectors (40, 42) are arranged within a distance forming the measuring path (B).

4. Apparatus according to claim 1 or 2, characterized in that the second capillary tube branch (100) comprises two detectors (114, 116) within a space forming the measuring path (B).

5. Apparatus according to claim 3 or 4, characterized in that the space forming the measuring path (B) amounts to 30-200 mm.

6. Apparatus according to any of claims 1 to 5, characterized in that the vertical space between the first capillary tube branch (24; 96) and the second capillary tube branch (28; 100) amounts to 40-160 mm.

7. Apparatus according to any of claims 1 to 6, characterized in that adjacent to the second capillary tube branch (100), respectively the third capillary tube branch (32) there is a rising capillary tube branch (102, respectively 34).

8. Apparatus according to any of claims 1 to 7, characterized in that adjacent to the first capillary tube branch (24) there is a substantially vertically rising capillary tube branch (22).

9. Apparatus according to any of claims 1 to 8, characterized in that at the downstream end of the second capillary tube branch (28) a third detector (46) for time depending control of a downstream arranged closure magnet (48) is arranged.

10. Apparatus according to any of claims 4 to 8, characterized in that streamup of the detectors (114,116) a fourth detector (112) is arranged within the groove (86) by the signal of which a syringe drive (110) arranged on the front plate and/or a cutting tool (118) for separating the capillary tube is operable.

11. Apparatus according to any of claims 1 to 11, characterized in that the flexible plastic hose (36; 104) consists of polyethylene or polyurethane having an inner diameter of about 0,5-2 mm and a wall thickness of about 0,2-0,5 mm.

12. Apparatus according to any of claims 1 to 11, characterized in that the front plate (12, 84) is temperature controllable to about 37°C.

13. Apparatus according to claim 7, characterized in that the rising capillary tube branch (34; 102) adjacent to the second (28; 100), respectively third capillary tube branch (32) comprises at least one curved capillary tube branch with substantially horizontal, parallel capillary tube sections (62, 70) and the upper capillary tube section (70) of the hose (36; 104) is connected with a three- way part (72) which is connected with a suction pump (76) via a conduit (74).

14. Apparatus according to claim 13, characterized in that within each of the horizontal capillary tube sections (62, 70) one detector (78, 82) is arranged by means of which the pressure value achieved with the suction pump (76) may be determined.

15. Apparatus according to claim 13 or 14, characterized in that the vertical space between the horizontal capillary tube sections (62, 70) amounts to 60-140 mm.

16. Apparatus according to any of claims 3 to 15, characterized in that the detectors (40, 42, 46, 78,82,112,114,116) are optoelectronical sensors.

Images